Can a positioned move teeth back after discontinued use?

I have had a positioner for a long time and had been wearing it regularly until about a year ago when my jaw started popping and moving irregularly. I discontinued use due to the pain and weird movement of my jaw. My jaw pain went away but unfortunately my teeth have moved. I started wearing my positioner again to correct it but it hurt my teeth very badly, is this normal? I want to get braces but money is tight. How can I keep my teeth in place in the meantime? Will wearing the positioner help?